In a mechanical seal used as a shaft seal device of a pump and the like, a first sliding member fixed to a shaft and a second sliding member fixed to a housing are brought into close contact with each other subject to an energizing force in an axial direction by a spring or the like and also slid each other by the rotation of the shaft. Thus, sliding properties have been enhanced by providing irregularities or grooves on the sliding surface of the sliding member.
For example, Patent Document 1 describes a mechanical seal that seeks to improve lubricity by forming fine irregularities having directional properties on the sliding surface of a sliding member by femtosecond laser beam machining to make it easier for a fluid to be sealed to flow to the sliding surface. Patent Document 2 describes a mechanical seal that seeks to reduce sliding resistance by generating dynamic pressure during shaft rotation by grooves formed on the sliding surface to draw more fluid to be sealed to the sliding surface (formation of a lubricating film by the fluid to be sealed).
Dynamic pressure that mitigates sliding resistance of a sliding member is not generated before the rotational speed of the shaft reaches a certain level of high speed. Thus, a sufficient amount of fluid to be sealed cannot be interposed between sliding surfaces before the rotational speed at which dynamic pressure is generated after the start of rotation, which could lead to lower lubricity. In such a state, the torque becomes high, seizing, vibration, or noise is generated, and sliding properties become unstable.